Method for manufacturing semiconductor device

Abstract

In a transistor including an oxide semiconductor film, a metal oxide film for preventing electrification which is in contact with the oxide semiconductor film and covers a source electrode and a drain electrode is formed. Then, oxygen is introduced (added) to the oxide semiconductor film through the metal oxide film and heat treatment is performed. Through these steps of oxygen introduction and heat treatment, impurities such as hydrogen, moisture, a hydroxyl group, or hydride are intentionally removed from the oxide semiconductor film, so that the oxide semiconductor film is highly purified. Further, by providing the metal oxide film, generation of a parasitic channel on a back channel side of the oxide semiconductor film can be prevented in the transistor.

The invention claimed is: 
     
       1. A method for manufacturing a semiconductor device, comprising the steps of:
 forming a gate electrode over a substrate; 
 forming a gate insulating film over the gate electrode; 
 forming an oxide semiconductor film overlapping with the gate electrode with the gate insulating film interposed therebetween; 
 forming a source electrode and a drain electrode over the oxide semiconductor film; 
 forming a metal oxide film comprising gallium over the source electrode and the drain electrode, the metal oxide film being in contact with the oxide semiconductor film; 
 introducing oxygen to at least one of the oxide semiconductor film, the metal oxide film, and an interface between the oxide semiconductor film and the metal oxide film; and 
 performing heat treatment. 
 
     
     
       2. A semiconductor device comprising:
 a gate electrode over a substrate; 
 a gate insulating film over the gate electrode; 
 an oxide semiconductor film overlapping with the gate electrode with the gate insulating film interposed therebetween; 
 a source electrode and a drain electrode over the oxide semiconductor film; and 
 a metal oxide film comprising gallium over the source electrode and the drain electrode, the metal oxide film being in contact with the oxide semiconductor film; 
 wherein oxygen is introduced to at least one of the oxide semiconductor film, the metal oxide film, and an interface between the oxide semiconductor film and the metal oxide film. 
 
     
     
       3. The semiconductor device according to  claim 2 , wherein the metal oxide film comprises gallium oxide. 
     
     
       4. The semiconductor device according to  claim 2 , wherein the metal oxide film further comprises indium and zinc. 
     
     
       5. The semiconductor device according to  claim 2 , further comprises an insulating film over the metal oxide film. 
     
     
       6. The semiconductor device according to  claim 2 , wherein the metal oxide film is a gallium oxide film containing 0.01 at.% to 5 at.% of indium or zinc. 
     
     
       7. The semiconductor device, according to  claim 2 , wherein the oxide semiconductor film comprises indium, gallium and zinc. 
     
     
       8. The semiconductor device, according to  claim 2 , wherein a carrier concentration of the oxide semiconductor film is less than 1 ×10 14  cm −3 . 
     
     
       9. The semiconductor device, according to  claim 2 , wherein an electron affinity of the oxide semiconductor film plus 0.1 eV is greater than an electron affinity of the metal oxide film. 
     
     
       10. A semiconductor device comprising:
 a gate electrode over a substrate; 
 a gate insulating film over the gate electrode; 
 an oxide semiconductor film overlapping with the gate electrode with the gate insulating film interposed therebetween; 
 a source electrode and a drain electrode over the oxide semiconductor film; and 
 a metal oxide film comprising gallium over the source electrode and the drain electrode, the metal oxide film being in contact with the oxide semiconductor film; 
 wherein a concentration of oxygen in a first region of at least one of the oxide semiconductor film, the metal oxide film and an interface between the oxide semiconductor film and the metal oxide film is higher than that in a second region of the oxide semiconductor film and the metal oxide film which does not include the first region. 
 
     
     
       11. The semiconductor device according to  claim 10 , wherein the metal oxide film comprises gallium oxide. 
     
     
       12. The semiconductor device according to  claim 10 , wherein the metal oxide film further comprises indium and zinc. 
     
     
       13. The semiconductor device according to  claim 10 , further comprises an insulating film over the metal oxide film. 
     
     
       14. The semiconductor device according to  claim 10 , wherein the metal oxide film is a gallium oxide film containing 0.01 at.% to 5 at.% of indium or zinc. 
     
     
       15. The semiconductor device, according to  claim 10 , wherein the oxide semiconductor film comprises indium, gallium and zinc. 
     
     
       16. The semiconductor device, according to  claim 10 , wherein a carrier concentration of the oxide semiconductor film is less than 1×10 14  cm −3 . 
     
     
       17. The semiconductor device, according to  claim 10 , wherein an electron affinity of the oxide semiconductor film plus 0.1 eV is greater than an electron affinity of the metal oxide film.